Conventionally, a retardation plate has been used in various liquid crystal displays in order to achieve optical compensation. As such a retardation plate, an optically uniaxial film or an optically biaxial film has been used, for example. The optically uniaxial film can be produced, for example, by forming a particular polyimide into a film. The optical uniaxiality of the film is derived from the nature of the polyimide itself, and the obtained film exhibits negative uniaxial optical characteristics (see H8(1996)-511812 A, for example). On the other hand, the optically biaxial film has an excellent optical compensation function. For example, when the optically biaxial film is arranged as an optical film between a liquid crystal cell and a polarizer of a liquid crystal display, it can enhance the display characteristics of the liquid crystal display, for example, by widening its viewing angle. On this account, in recent years, instead of the optically uniaxial film, the optically biaxial film is used as a retardation plate more and more widely. The optically biaxial film can be produced, for example, by various polymer film stretching methods (see H3(1991)-33719 A, for example) and biaxially stretching methods (see H3(1991)-24502 A, for example). Also, there has been known a retardation plate in which a uniaxially stretched polymer film having a positive optical anisotropy and a biaxially stretched polymer film having a negative optical anisotropy and whose in-plane retardation is small are used in combination (see H4(1992)-194820 A, for example).